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| United States Patent |
5,339,381
|
|
Ikeda
, et al.
|
August 16, 1994
|
Optical fiber composite insulators
Abstract
An optical fiber composite insulator includes an insulator body in which a
through hole having a substantially radially circular cross section is
provided, a plurality of optical fibers passed through the through hole,
and an organic insulating material gas-tightly sealing the optical fibers
in the through hole, wherein a diameter of the through hole is not more
than 13 mm, the optical fibers are located inside a hypothetical circle
drawn on any plane orthogonal to an axis of the through hole and having a
center coaxial with that of the through hole, the hypothetical circle
having a diameter equal to 95% of that of the through hole, and a distance
between any optical fibers is set at not less than 0.1 mm.
| Inventors:
|
Ikeda; Mitsuji (Nagoya, JP);
Mine; Ryoichi (Nagoya, JP);
Nozaki; Masayuki (Ama, JP);
Sugiura; Tadashi (Okazaki, JP)
|
| Assignee:
|
NGK Insulators, Ltd. (JP)
|
| Appl. No.:
|
033751 |
| Filed:
|
March 18, 1993 |
Foreign Application Priority Data
| Mar 23, 1992[JP] | 4-064765 |
| Mar 23, 1992[JP] | 4-065276 |
| Mar 24, 1992[JP] | 4-065784 |
| Mar 24, 1992[JP] | 4-065787 |
| Mar 24, 1992[JP] | 4-066017 |
| Current U.S. Class: |
385/138; 174/139; 174/151; 385/100; 385/134; 385/147 |
| Intern'l Class: |
G02B 006/36 |
| Field of Search: |
385/100,101,123,134-139,147
174/138 R,139,151,152 R
|
References Cited
U.S. Patent Documents
| 4756596 | Jul., 1988 | Ona et al. | 385/110.
|
| 4921322 | May., 1990 | Seike et al. | 385/138.
|
| 5029969 | Jul., 1991 | Seike et al. | 350/96.
|
| 5069525 | Dec., 1991 | Seike et al. | 385/100.
|
| 5090793 | Feb., 1992 | Seike et al. | 385/100.
|
| 5109466 | Apr., 1992 | Seike et al. | 385/137.
|
| 5127083 | Jun., 1992 | Ikeda et al. | 385/138.
|
| 5136680 | Aug., 1992 | Seike et al. | 385/139.
|
| 5138692 | Aug., 1992 | Ikeda et al. | 385/138.
|
| Foreign Patent Documents |
| 0297728 | Jan., 1989 | EP | .
|
| 0364288 | Apr., 1990 | EP | .
|
| 60-158402 | Oct., 1985 | JP.
| |
Other References
Patent Abstracts of Japan, unexamined applications, P field, vol. 9, No.
334, Dec. 27, 1984 The Patent Office Japanese Government p. 124 P 417 *
No. 59-12 973 & JP-A-60-158 402 (Fujikura Densen K.K.), Aug. 19, 1985.
|
Primary Examiner: Gonzalez; Frank
Attorney, Agent or Firm: Parkhurst, Wendel & Rossi
Claims
What is claimed is:
1. An optical fiber composite insulator comprising an insulator body in
which a through hole having a substantially radially circular cross
section is provided, a plurality of optical fibers passed through said
through hole, and an organic insulating material gas-tightly sealing the
optical fibers in the through hole, wherein a diameter of said through
hole is not more than 13 mm, said optical fibers are located inside a
hypothetical circle drawn on any plane orthogonal to an axis of the
through hole and having a center coaxial with that of said through hole,
said hypothetical circle having a diameter equal to 95% of that of the
through hole, and a distance between any optical fibers is not less than
0.1 mm.
2. The optical fiber composite insulator claimed in claim 1, wherein said
organic insulating material is swelled out from each end face of the
insulator body to form a swelled portion, and a height from said end face
to a tip of said swelled portion is set at not more than 40 mm.
3. The optical fiber composite insulator claimed in claim 2, wherein said
swelled portion comprises a discoidal or frusto-conical portion, and a top
portion provided on a central portion of said discoidal or frusto-conical
portion, and a height of said top portion is not more than 5 mm.
4. The optical fiber composite insulator claimed in claim 3, wherein said
top portion has a columnar shape, and a radius of a tip face of the top
portion is not less than 3 mm.
5. The optical fiber composite insulator claimed in claim 2, wherein a
bonded length from an outer peripheral edge of the through hole at the end
face to an outer peripheral edge of a bonded portion of said swelled
portion to the end face is not less than 1 mm and not more than 35 mm.
6. The optical fiber composite insulator claimed in claim 2, wherein a
non-sealed portion of each of said optical fibers not sealed with the
organic insulating material and projecting outwardly from said insulator
body is inserted into a protective tube, said optical fiber being exposed
between an end face of said protective tube and an end face of the organic
insulating material, a holder with insertion holes is fixed to the end
face of the organic insulating material, locations of said insertion holes
being aligned with locations through which the optical fibers are taken
out, and exposed portions of the optical fibers and a part of said
protective tubes are held in said respective insertion holes.
7. The optical fiber composite insulator claimed in claim 6, wherein said
holder is fixed to said organic insulating material with an adhesive.
8. The optical fiber composite insulator claimed in claim 6, wherein a
cylindrical member is arranged around an outer periphery of said holder,
said cylindrical member is bonded to the organic insulating material, and
the holder is fixed to the organic insulating material by said cylindrical
member bonded to the organic insulating material.
9. The optical fiber composite insulator claimed in claim 6, wherein said
holder is comprised of a rubbery elastic material, and a diameter of said
insertion hole is smaller than an outer diameter of said protective tube.
10. The optical fiber composite insulator claimed in claim 6, wherein a
molding layer is provided around said protective tubes at a side of an end
face of said holder.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to optical fiber composite insulators and
processes for producing the same.
(2) Related Art Statement
a) Power transmission lines and power substations require systems for
rapidly detecting locations of any troubles occurring in the power
transmission lines or the power substations due to lighting, etc. and for
restoring the systems. Therefore, abnormal current or abnormal voltage
detectors utilizing optical sensors having Faraday effects and Pockels
effect have been used. In these detectors, it is necessary to insulate the
voltage and current in the power transmission between the sensor attached
to a power transmission line and the troubled location detector. For this
purpose, optical fiber composite insulators in which optical fibers are
placed are used to transmit optical signals only and maintain electrical
insulation.
As such optical fiber composite insulators, it is a common practice that a
slender through hole is provided in the insulator body thereof, an optical
fiber is passed through this through hole, and the optical fiber is sealed
in the through hole with an organic insulating material such as silicone
rubber or an epoxy resin. However, there is a problem in that the organic
insulating material is largely shrunk at low temperatures in the winter
season so that the optical fiber is warped to increase loss in the light
transmission. Further, there is another problem in that the organic
insulating material does not go around the optical fiber if organic
insulating material-pouring conditions are not properly kept during the
production of the optical fiber composite insulator so that poorly adhered
locations are likely to be formed to reduce insulating performance.
b) Moveover, Japanese Utility Model Registration Laid-open No. 64-31,620
proposed an optical fiber composite insulator in which a through hole is
provided in a slender insulator body, an optical fiber is passed through
the through hole, and an organic insulating material is filled in this
through hole in the state that the organic insulating material is swelled
up from end faces 2 of the insulator body. This is to absorb expansion of
the organic insulating material with the swelled portions of the organic
insulating material so that swelling of the interior organic insulating
material itself out of the through hole and consequent breakage of the
optical fiber may be prevented. Since the expanded amount of the organic
insulating material is great at high temperatures, it is a common practice
that the organic insulating material is largely swelled up to absorb the
expansion as much as possible.
However, such optical fiber composite insulators also have a problem in
that the light transmission loss increases particularly at low
temperatures. Furthermore, the insulators have another problem in that
adhesion forces decrease between the swelled-up portion made of the
organic insulating material and the end face of the insulator body, when
the insulator undergoes temperature changes over an extended time period.
c) Furthermore, NGK proposed an optical fiber-holding structure as an
optical fiber composite insulator in Japanese Utility Model Registration
Application No. 3-87,080 (filed on Sept. 27, 1992, not published)
schematically shown in FIG. 1. This structure will be briefly explained.
A through hole 1a is provided in a central portion of an insulator body 1,
and for example, two optical fibers 2 are passed through the through hole
1a. Optical fibers 2 are gas-tighly sealed inside the through hole 1a with
an organic insulating material 3. In the embodiment of FIG. 1, the organic
insulating material 3 is swelled up from an end face 1b of the insulator
body 1 to form a swelled portion 4. This swelled portion 4 consists of
three portions. That is, a frusto-conical portion 4a is concentrically
formed around the through hole 1a, a columnar top portion 4c is formed on
a central portion of the frusto-conical portion 4a, and a relatively thin
extended portion 4b is formed at a skirt of an outer peripheral edge of
the frusto-conical portion 4a. The optical fibers 2 are passed through the
frusto-conical portion 4a and the columnar top portion 4c, and comes out
from an end face 4d of the columnar top portion 4c.
A peripheral side face of the columnar top portion 4c is covered with a
cylindrical pipe 22. Portions of the optical fibers 2 not sealed with the
organic insulating material are passed through protective tubes 25. Parts
of the optical fibers are exposed between end faces of the protective
tubes 25a and the end face 4d of the columnar top portion 4c. A molding
adhesive is poured and filled into the pipe 14, thereby forming a molding
layer 24. The exposed portions 2a of the optical fibers and the near end
faces of the protective tubes 7 are fixed and held inside the molding
layer 24.
However, it is first discovered that such a holding structure has the
following problems.
That is, since the optical fibers 2 and the tip portions of the protective
tubes 25 are directly fixed inside the molding layer 24, it may be that
the optical fibers 2 are fixed in a bent shape at the exposed portions 2a
thereof (particularly, at a portion P shown) when the molding adhesive is
poured between the end face of the columnar top portion 4c and the tip
portions of the protective tubes 25, so that excess load is applied to the
optical fiber 2 in some cases. Further, since the protective tubes may not
be sufficiently fixed, excess load is exerted upon the optical fibers
particularly at the portion P when the protective tubes are bent or sway.
d) In the optical fiber composite insulators, one or more optical fibers
are passed through the through hole provided in the insulator body, the
organic insulating material is filled in the through hole, and the organic
insulating material is cured by heating. As is known, the curing
temperatures of the organic insulating materials range from room
temperature to beyond 100.degree. C. For example, Japanese Patent
Application Laid-open No. 2-106,823 discloses that the curing temperature
is set at not less than 60.degree. C. when the organic insulating
materials is silicone rubber. Further, in order to cure the organic
insulating material by heating, it is known that after the organic
insulating material is filled into the insulator body at room temperature,
the organic insulating material is cured by heating the entire insulator.
The organic insulating material filled in the through hole of the insulator
expands or shrinks with changes in the surrounding temperature. At that
time, the organic insulating material expands following the expansion on a
temperature side higher than the curing temperature of the organic
insulating material so that the optical fiber undergoes compression in a
radial direction of the insulator. Therefore, when the insulator is heated
to high temperatures through direct irradiation of sunlight in the summer
or passage of current, the optical fiber is finely warped (microbending)
due to expansion of the organic insulating material when the curing
temperature is too low. Consequently, the light transmission loss
increases. To the contrary, when the insulator is cooled to low
temperatures with cold wind in the winter season or other reason and the
curing temperature of organic insulating material is too high, the organic
insulating material is shrunk to cause the optical fiber to be finely
warped (microbending), so that the light transmission loss becomes
greater, too.
Furthermore, when the entire insulator is heated after the organic
insulating material is filled into the insulator body at room temperature,
it takes a long time to heat the insulator to a given temperature because
the heat capacity of the insulator is large. Consequently, the organic
insulating material is cured at a temperature lower than the intended
curing temperature, so that the light transmission loss becomes greater
when the insulator is heated to high temperatures.
Furthermore, the optical fiber is finely bent (microbending) with a
pressure exerted upon the fiber on filling the fluidizing organic
insulating material by the shrinkage of the organic insulating material on
curing, so that the sealing is effected in some cases in the state that
the optical fiber is kept bent. If the optical fiber is sealed in the bent
state, stress concentrates upon a bent portion of the optical fiber. As a
result, the light transmission loss of the optical fiber increases,
fatigue fracture is likely to occur due to expansion and shrinkage of the
organic insulating material with changes in the surrounding temperature,
and service life of the optical fiber decreases.
SUMMARY OF THE INVENTION
The present invention solves the above-mentioned problem in (a), and is
aimed at improving the light transmission performance at low temperatures
and insulating performance of the optical fiber composite insulator.
A first aspect of the present invention relates to an optical fiber
composite insulator in which a through hole having a substantially
circular cross sectional shape as viewed in a diametrical direction is
provided in an insulator body, a plurality of optical fibers are passed
through the through hole, and the optical fibers are gas-tightly sealed
with an organic insulating material, wherein the diameter of the through
hole is not more than 13 mm, the optical fibers are located inside a
hypothetical circle having a coaxis with the through hole and a diameter
being 95% of that of the through hole, and a distance between the optical
fibers is not less than 0.1 mm.
A second aspect of present invention solves the above-mentioned problems in
(b), and is aimed at reducing the light transmission loss of the optical
fiber composite insulator of the type in which the optical fibers are
sealed with the organic insulating material. Further, the invention is
also aimed at separation between a swelled portion of the organic
insulating material and an end face of the insulator body at an bonding
interface. Furthermore, such an optical fiber composite insulator is
produced at a high efficiency without exerting adverse effects upon the
light transmission performance of the optical fiber.
According to the second aspect of the present invention which is to improve
the optical fiber composite insulator of the first aspect of the
invention, the organic insulating material is swelled up outwardly from
the end face of the insulator body to form a swelled portion, and the
height of the swelled portion of the insulating material from the end face
of the insulator body to the tip of the swelled portion is set at not more
than 40 mm.
Further, the second aspect of the present invention improves on the optical
fiber composite insulator of the first aspect of the present invention,
and is directed to the optical fiber composite insulator in which the
organic insulating material is swelled up outwardly from the end face of
the insulator body to form a swelled up outward portion, and a bonded
length from an outer peripheral edge of the through hole at the end face
of the insulator body to the outer peripheral edge of the bonded portion
of the swelled portion to the end face of the insulator body is set at not
less than 1 mm and not more than 35 mm.
A third aspect of the present invention solves the above-mentioned problems
in (c), and is aimed at preventing application of an excess load upon the
optical fibers taken out near the end face of the organic insulating
material and to reduce resulting light transmission loss.
The third aspect of the present invention improves on the optical fiber
composite insulator of the first aspect of the present invention, and
relates to the optical fiber composite insulator in which portions of the
optical fibers projecting outwardly from the insulator body and not
covered with the organic insulating material are passed through respective
protective tubes, the optical fibers are exposed between one end face of
the protective tubes and an end face of the organic insulating material, a
holder having insertion holes is fixed to the end face of the organic
insulating material, optical fiber-taken out locations are aligned with
the respective insertion holes of the holder, and the exposed portions of
the optical fibers and the protective tubes are partially held inside the
insertion holes.
A fourth aspect of the present invention solves the above-mentioned
problems in (d), provides a process for producing optical fiber composite
insulators, which can prevent the microbending of the optical fibers and
realize excellent light transmission performance and durability.
The fourth aspect of present invention provides a process for producing
optical fiber composite insulators in which a through hole is provided in
an insulator body, at least one optical fiber is passed through the
through hole, and at least one optical fiber is sealed with an organic
insulating material, wherein after the entire insulator body is
preliminarily heated to not less than 70.degree. C., the organic
insulating material is filled into the through hole of the insulator body
in the state that the optical fiber passed through the through hole is
stretched straight, and the filled organic insulating material is cured at
not less than 75.degree. C. to not more than 95.degree. C. by heating in
the state that the at least one optical fiber is kept stretched straight
until the organic insulating material is cured.
In the above construction, when the organic insulating material is heated
at not less than 75.degree. C. to not more than 95.degree. C., the light
transmission loss due to expansion of the organic insulating material at
high temperatures and due to shrinkage of the organic insulating material
at low temperatures can be prevented. Thus, the optical fiber composite
insulator having excellent light transmittability over a range of the
temperatures changeable in use environment of the insulator can be
obtained. Further, after the entire insulator body is preliminarily heated
up to not less than 70.degree. C., the organic insulating material is
filled in the through hole of the insulator body and the organic
insulating material is cured by heating. Consequently, the organic
insulating material is assuredly cured in a temperature range of not less
than 75.degree. C. but not more than 90.degree. C. by heating, so that the
optical fiber composite insulator having excellent light transmittability
can be obtained. As will be clear from examples given later, the reason
why the curing temperature of the organic insulating material is limited
to not less than 75.degree. C. but not more than 90.degree. C. and the
reason why the preliminarily heating temperature is limited to not less
than 70.degree. C. are to suppress light transmission loss which cannot be
attained at temperatures outside these ranges.
These and other objects, features and advantages of the invention will be
understood from the following description of the invention when taken in
conjunction with the attached drawings, with the understanding that some
modifications, variations and changes of the same could be made by the
skilled person in the art to which the invention pertains without
departing from the spirit of the invention or the scope of claims appended
hereto.
BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS
For a better understanding of the invention, reference is made to the
attached drawings, wherein:
FIG. 1 is a sectional view of a principle portion of an optical fiber
composite insulator as a reference example;
FIG. 2 is a sectional enlarged view of an optical fiber composite insulator
according to the first aspect of the present invention near an end face
thereof;
FIG. 3a is a schematically sectional view of the optical fiber composite
insulator as cut in a diametrical direction of a through hole 1a for the
illustration of a construction of the first aspect of the present
invention, and FIG. 3b is a similar sectional view of a modification of
the optical fiber composite insulator in FIGS. 2 and 3a;
FIG. 4 is a sectional view illustrating a state in which molds 7 are set at
respective end faces 1c of an insulator body 1 and an organic insulating
material 3B is filled;
FIG. 5 is a graph showing the relationship between the diameter of the
through hole and the depressed amount of the organic insulating material;
FIG. 6 is a graph showing the relationship between the diameter of the
through hole and the light transmission loss;
FIG. 7 is a sectional enlarged view for illustrating a portion of another
optical fiber composite insulator near an end face 1c;
FIG. 8 is a sectional view for schematically illustrating the entire
optical fiber composite insulator;
FIG. 9 is a sectional view for schematically illustrating a still another
optical fiber composite insulator in its entirety;
FIG. 10 is a sectional view for schematically illustrating a further
optical fiber composite insulator near an end face 1c;
FIG. 11 is a sectional view for illustrating a still further optical fiber
composite insulator near an end face 1c;
FIG. 12 is a sectional view for illustrating a still further optical fiber
composite insulator near an end face 1c;
FIG. 13 is a sectional view for illustrating a state in which molds 7 are
fitted to an insulator body 1 and an organic insulating material 3B is
poured;
FIG. 14 is a graph showing the relationship between the height H of the
swelled portion and the light transmission loss at 0.degree. C. or
-20.degree. C.;
FIG. 15 is a graph showing the relationship between the height of the top
of the swelled portion and the light transmission loss at 80.degree. C. or
-20.degree. C.;
FIG. 16 is a sectional enlarged view of a principal portion of a further
embodiment of the optical fiber composite insulator according to the
present invention;
FIG. 17 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 18 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 19 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 20 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 21 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 22 is a sectional enlarged view of a principal portion of a still
further embodiment of the optical fiber composite insulator according to
the present invention;
FIG. 23 is a graph showing the relationship between the curing temperature
of the organic insulating material and the light transmission loss; and
FIG. 24 is a graph showing the relationship between the elongation and
changes in the light transmission loss when the optical fiber is
stretched.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a sectional view of an optical fiber composite insulator near an
end face in an enlarged scale.
An insulator body 1 has a slender columnar shape, and a number of sheds are
provided around an outer peripheral surface of the insulator body 1. A
through hole 1a having an almost circular sectional shape as viewed in a
diametrical direction is formed in a central portion of the insulator body
1. Through the through hole 1a are passed, for example, two optical fibers
2A and 2B. Outer peripheral portions of the insulator body 1 are fitted to
respective flanges 6 through a cement layer 5 at upper and lower ends of
the insulator body. An organic insulating material 3A is filled into the
through hole 1a. Further, the organic insulating materials is swelled up
outwardly from an end face 1c at each of upper and lower ends of the
insulator body 1 to form a swelled portion 4A.
In the embodiment of FIG. 2, the swelled portion 4A has a flat discoidal
shape. The optical fibers 2A and 2B are taken out upright from the central
portion of the discoidal swelled portion 4A.
FIG. 3(a) is a sectional view of the through hole 1a as cut in the
diametrical direction. In FIG. 3(a), the organic insulating material 3A is
omitted for facilitating understanding this figure.
According to the present invention, the diameter of the through hole 1a is
set at not more than 13 mm. The center of a hypothetical circle C is
concentric with the center O of the through hole 1a, and the diameter of
the hypothetical circle C is set at not less than 95% of that of the
through hole 1a. Such a hypothetical circle is drawn on any plane
orthogonal to an axis of the through hole. The optical fibers 2A and 2B
are located inside the hypothetical circle. The distance between the
optical fibers 2A and 2B is set at not less than 0.1 mm.
By adopting the above construction, the following effects can be obtained.
That is, the present inventors have acquired the following knowledge
through various investigations of causes which increase the light
transmission loss at low temperatures. As the organic insulating material
3A, silicone rubber, urethane rubber, epoxy resin or the like is
concretely employed. Among them, particularly silicone rubber is preferred
because the rubber has excellent stress-mitigating action. Since these
organic insulating materials have coefficients of thermal expansion being
a few to a several tens times as great as that of the insulator body, the
organic insulating material greatly shrinks inside the through hole at low
temperatures. However, since the organic insulating material 3A inside the
through hole 1a is firmly bonded to the wall surface of the insulator body
1, the movement of the organic insulating material is so restricted that
the insulating material will not substantially shrink in a diametrical
direction or in a circumferential direction of the through hole, whereas
the insulating material largely shrinks only in the axial direction near
end portions of the through holes 1a. Thus, when the organic insulating
material 3A is displaced (i.e. depressed) near the end portions of the
through hole 1a, the optical fibers 2A and 2B sealed with the insulating
material are shrunk to cause the light transmission loss.
Under these circumstances, according to the present invention, it is
acknowledged that when the diameter of the through hole 1a is set at not
more than 13 mm, the displacement (depression) of the organic insulating
material near the end portions of the through hole 1a at the low
temperatures can be reduced.
The reason is considered as follows:
Since the organic insulating material 3A is bonded to the wall surface of
the through hole 1a, this serves to restrict the axial shrinkage of the
organic insulating material 3A. Such an effect becomes greater as the
location approaches the wall surface of the through hole, whereas the
effect becomes weaker as the location approaches the center of the through
hole. Therefore, as the diameter of the through hole becomes smaller, the
movement-restricting effect acts near the central portion of the through
hole. As mentioned above, since the movement inside the through hole in
the diametrical direction and the circumferential direction is restricted,
the shrinkage of the organic insulating material sealingly filled in the
through hole 1a concentratedly occurs as a displacement in the axial
direction near the end portions of the through hole 1a. Consequently, even
if the shrinkage factor of the organic insulating material is constant,
the greater the diameter of the through hole 1a, the greater is the
depressed amount (maximum value) of the insulating material in the axial
direction. It is considered that the axial displacement of the insulating
material is substantially proportional to 1.5-2 (the diameter of the
through hole 1a). Therefore, as the diameter of the through hole becomes
smaller, the displacement (depressed amount) of the organic insulating
material near the end portion becomes smaller.
Further, according to the present invention, since the optical fibers 2A
and 2B are located inside the hypothetical circle C, the optical fibers 2A
or 2B will not contact the wall surface of the through hole 1a, and the
organic insulating material 3A can be sufficiently filled between the
optical fibers and the wall surface of the through hole. In addition,
since the distance between the optical fibers 2A and 2B is set at not less
than 0.1 mm, the organic insulating material 3A can be fully filled around
the optical fibers 2A and 2B. By restricting the diameter of the
hypothetical circle and the distance between the optical fibers as
mentioned above, the organic insulating material can be uniformly
distributed all around the optical fibers 2A and 2B, and insufficiently
bonded portions do not occur. As a result, the insulating performance
against the optical fibers can be enhanced.
The above restrictions are also applicable in the case where three or more
optical fibers are passed through the through hole. For example, a case in
which four optical fibers are employed will be explained with reference to
FIG. 3b. The optical fibers 2A, 2B, 2C 2D are passed through the through
hole 1a. In that case, it is necessary that the optical fibers 2A, 2B, 2C
and 2D are all located inside the hypothetical circle C such that each of
l.sub.AB, l.sub.BC, l.sub.CD, l.sub.DA, l.sub.AC and l.sub.BD is set at
not less than 0.1 mm in which l.sub.AB is a distance between the optical
fibers 2A and 2B, l.sub.BC is a distance between the optical fibers 2B and
2C, l.sub.CD is a distance between the optical fibers 2C and 2D, l.sub.DA
is a distance between the optical fibers 2D and 2A, l.sub.AC is a distance
between the optical fibers 2A and 2C, and l.sub.BD is a distance between
the optical fibers 2B and 2D.
Next, a preferred process for producing the optical fiber composite
insulators as shown in FIGS. 2, 3a and 3b will be explained below with
reference to FIG. 4.
A mold 7 is placed on each of the end faces 1c of the insulator body 1. A
swelled portion-forming space 7a is formed in the mold 7, and a through
hole 7b is communicated with the swelled portion-forming space 7a. An
organic insulating material-feeding pipe 9A is fitted to the lower mold 7,
and an organic insulating material discharge pipe 9B is fitted to the
upper mold 7. The interior of each of the pipe 9A and 9B is communicated
with the through hole 7b. The mold 7 is fixed to a flange by using bolts
10, and the mold 7 and the end face 1c are gas-tightly sealed by using an
O-ring 13. An insertion hole 7c is provided in a central portion of the
mold 7 for passing the optical fibers therethrough. When the mold 7 is set
to the end face of the insulator body, the center of the mold 7 is aligned
with that of the through hole 1a.
In order to prevent contact between the optical fibers 2A and 2B inside the
through hole 1a and contact between the optical fibers and the wall
surface of the through hole 1a, it is preferable that the optical fibers
2A and 2B are preliminarily fixed with spacers 12 made of the same
material as that of the organic insulating material 3A at three or more
locations. The optical fibers 2A and 2B are geometrically arranged
according to the present invention.
The optical fibers 2A and 2B are passed through the through hole 7c and the
through hole 1a. A packing 8 is fitted to the through hole 7c of the mold
7. In order to prevent contact between the optical fibers 2A and 2B and
contact between the optical fibers and the wall surface of the through
hole 1a near the end portion of the through hole 1a, it is preferable that
two through holes having substantially the same diameter as that of the
optical fiber are provided in the packing 8 such that the locations of
these through holes are adjusted to prevent positional deviation of the
optical fibers 2A and 2B.
Further, it is preferable that the optical fibers are stretched straight by
applying a tensile load to each of the optical fibers 2A and 2B. By so
doing, even when the organic insulating material 3B is filled, the
contacting between the optical fibers and the contacting between the
optical fibers and the wall surface of the through hole can be assuredly
prevented. Further, it is possible to prevent the optical fibers from
being finely bent due to pressure under which the organic insulating
material 3B is filled.
In order that bubbles may not be taken into the organic insulating material
3B during pouring, it is preferable that the interior of the through hole
1a is preliminarily evacuated to a reduced pressure of 1 to 3 torrs, and
then the organic insulating material 3B is fed through the
material-pouring pipe 9A. The insulating material 3B goes up inside the
through hole 1a, and reaches the material discharge opening 9B. The
swelled portion-forming space 7a and the through hole 1a are filled with
the organic insulating material, which is cured by heating. Then, the
molds are removed.
At that time, when the pouring pressure for the organic insulating material
3B is set at 3 to 10 kgf/cm.sup.2, the insulating material can be easily
uniformly poured into the through hole 1a.
In the following, specific experimental results will be explained.
EXPERIMENT 1
Optical fiber composite insulators as shown in FIGS. 2 and 3(a) were
produced by the above-mentioned method shown in FIG. 4. The dimensions of
the insulator body 1 were 1,150 mm in a total length, 105 mm in a barrel
diameter, and 205 mm in a shed diameter. In this experiment, the height h
of a swelled portion 4A was set at 3 mm, and a depressed amount of an
organic insulating material in a central portion was measured. As optical
fibers 2A and 2B, quartz base optical fiber filaments were used. As the
organic insulating material 3B, liquid silicone rubber, which had a
viscosity of 500 to 1,000 poises before curing, was used.
The diameter of the through hole 1a of the insulator bodies 1 were varied
in various ways as shown in FIGS. 5 and 6, and the average displacement
(depressed amount) of the organic insulating material at the end face at
-20.degree. C. and the light transmission loss at -20.degree. C. were
measured with respect to each insulator. Results are shown in FIGS. 5 and
6. The light transmission loss at -20.degree. C. was obtained as a ratio
of a light-transmitted amount at -20.degree. C. to that at room
temperature (25.degree. C.).
In this experiment, the optical fibers 2A and 2B were arranged through a
circumference of a hypothetical circle coaxial with the through hole 1a
and 30% of the diameter of the through hole 1a, while the optical fiber 2A
was point-symmetrical with the optical fiber 2B around the center O of the
through hole. Therefore, when the diameter of the through hole 1a is 4 mm,
the distance between the optical fibers 2A and 2B is 1.2 mm.
As is seen from FIG. 6. the light transmission loss at -20.degree. C.
rapidly increased at a point of time when the diameter increased to 13 mm.
Further, as the diameter of the through hole increases, the depressed
amount of the organic insulating material increases.
EXPERIMENT 2
Optical fiber composite insulators as shown in FIG. 3 were produced by the
above-mentioned method shown in FIG. 4. The dimensions of the insulator
body 1 were 1,150 mm in a total length, 105 mm in a barrel diameter, and
205 in a shed diameter. As optical fibers 2A and 2B, quartz base optical
fiber filaments were used. The outer diameter of the coated fiber filament
with an ultraviolet ray-curable resin was 0.4 mm. As an organic insulating
material 3B, liquid silicone rubber having a viscosity of 500 to 1,000
poises before curing was used.
Arrangement of the optical fibers 2A and 2B were changed in various ways,
and insulating performance of the optical fiber composite insulators was
evaluated.
Concretely, the distance between the optical fibers 2A and 2B were varied
as shown in Table 1 . At the same time, a hypothetical circle passing
either the optical fiber 2A and 2B remoter from the center O and having
the center O of the through hole as its center was taken, and a ratio of
the diameter of the hypothetical circle to that of the through hole was
varied as shown in Table 1. With respect to each sample in Table 1, five
insulator bodies with the through holes 1a each having the diameter of 6
mm and five insulator bodies with the through holes each having the
diameter of 10 mm were prepared, and tested. That is, a total of ten
insulator bodies were prepared for each sample.
As a standard sample, five insulator bodies with the through holes 1a each
having the diameter of 6 mm and five insulator bodies with the through
holes 1a each having the diameter of 10 mm were also prepared, and tested.
That is, a total of ten insulator bodies were prepared for the standard
sample. In each of the insulators as the standard sample, only one optical
fiber was passed through the center of the through hole 1a such that the
optical fiber might not contact the wall surface of the through hole.
Insulating performance was evaluated by measuring the flashover voltage of
each of the optical fiber composite insulators, determining the average
flashover voltage of the ten insulators, and relatively evaluating it with
reference to the average value of the standard sample being taken as 1.0.
As a reference sample, two optical fibers were contacted with each other
and the optical fibers were also contacted with the wall surface of the
through hole, which was considered to deteriorate greatly the insulating
performance. With respect to the reference sample, a total of ten
insulators were prepared as mentioned above, and their relative values of
the flashover voltages were measured to be 0.70.
Relative values of the flashover voltages of the Standard sample, Invention
samples, Comparative samples and Reference sample are shown in Table 1.
TABLE 1
__________________________________________________________________________
Ratio of the diameter of
a hypothetical circle
encompassing the optical
Minimum distance
Flashover
fibers to that of the
between optical
voltage
through hole fibers (relative
(%) (mm) value)
__________________________________________________________________________
Standard
-- -- 1.00
Sample
Invention
50 0.2 1.00
samples 70 0.5 1.00
90 0.1 0.95
95 0.3 0.97
Comparative
97 0.2 0.83
samples 80 0.05 0.79
Reference
The optical fiber(s)
The optical
0.70
samples contacted the wall of the
fibers contacted
through hole.
each other
__________________________________________________________________________
As is seen from Table 1, when the diameter of the hypothetical circle on
which the remoter optical fiber is located becomes 97% of the diameter of
the through hole, insulating performance drops. The insulating performance
is also deteriorated when the distance between the optical fibers 2A and
2B was 0.05 mm. In addition, it is more preferable that the diameter of
the hypothetical circle on which the remoter optical fiber is located is
not more than 70% of the diameter of the through hole. Furthermore, it is
more preferable that the distance between the optical fibers is not less
than 0.2 mm.
As mentioned above, according to the present invention, since the diameter
of the through hole is not more than 13 mm, the displacement (depressed
amount) of the organic insulating material near the end portion of the
through hole at low temperatures can be reduced and the light transmission
loss at low temperatures can be reduced. In addition, since the optical
fibers are located inside the hypothetical circle having the diameter
being 95% of that of the through hole, the contacting between the optical
fibers and the wall surface of the through hole can be prevented, and the
organic insulating material can fully go around between the optical fibers
and the wall surface of the through hole. Further, since the distance
between any two optical fibers is set at not less than 0.1 mm, the organic
insulating material can fully be distributed around between the optical
fibers. As a result, since the organic insulating material can fully go
around the optical fibers, insufficient contact between the organic
insulating material and the optical fibers can be prevented to improve the
insulating performance for the optical fibers.
Then, the second aspect of the present invention will be explained below.
FIG. 7 is a sectional view illustrating an optical fiber composite
insulator near an end face in an enlarged scale, and FIG. 8 is a sectional
view illustrating another entire optical fiber composite insulator.
An insulator body 1 has a slender columnar shape, and is provided with a
number of sheds 1b at its outer peripheral surface. A circular-section
through hole 1a is formed in a central portion of the insulator body 1.
Through the through hole 1a are passed, for example, two optical fibers 2.
Each of upper and lower surface portions of the insulator body 1 is fitted
to a flange 6 through a cement layer 5 at an outer peripheral portion. An
organic insulating material 3A is filled into the through hole 1a. The
organic insulating material 3A is swelled up outwardly from the end face
1c at each of the upper and lower ends of the insulator body 1 to form a
swelled portion 4A.
In the embodiment of FIG. 7, the swelled portion 4A consists of three
portions. That is, a frusto-conical portion 4a is formed concentrically
with the through hole 1a, and a columnar top portion 4c is formed on a
central portion of the frusto-conical portion 4a. A relatively thin
extension portion is formed at a skirt portion of the outer peripheral
edge of the frusto-conical portion 4a. The optical fibers 2 are passed
through the frusto-conical portion 4a and the cylindrical columnar top
portion 4c, and taken out through a tip end face of the columnar top
portion 4c.
The present inventors have made various investigations on causes which
increase the light transmission loss at low temperatures, and obtained the
following knowledge.
As the organic insulating material, silicone rubber, urethane rubber, epoxy
resin or the like may be concretely used. since these organic insulating
materials have coefficients of thermal expansion being a few to several
tens times as great as that of the insulator body, the swelled portion of
the organic insulating material is greatly shrunk at low temperatures. On
the other hand, since the organic insulating material inside the through
hole is firmly bound to the wall surface of the through hole of the
insulator body, the movement of the insulating material is so restricted
that the insulating material cannot so shrink even at low temperatures.
As mentioned above, it has been a conventional practice to absorb the
expansion of the insulating material at high temperatures by increasing
the height of the swelled portion. However, the swelled portion is largely
shrunk at low temperatures so that strain occurs inside the organic
insulating material near an opening at the end of the through hole. As a
result, microbending occurs in the optical fibers sealed near the opening
at the end of the through hole, which causes the light transmission loss.
Based on the above knowledge, the present inventors have discovered that
when the height H from the end face 1c of the insulator body 1 to the tip
of the swelled portion 4A is set at not more than 40 mm, the light
transmission loss at low temperatures can be largely reduced. The reason
why such an effect can be obtained is considered that when the height H is
thus restricted, the strain inside the organic insulating material near
the opening at the end of the round through hole 1a can be largely reduced
even at low temperatures, and the microbending of the optical fibers there
can be prevented.
Furthermore, the present inventors have made various investigations on
causes to reduce bonding forces on long-term use at the bound interface
between the swelled portion made of the organic insulating material and
the end face of the insulator body, and discovered that the bonded length
l from the outer peripheral edge A of the through hole 1a to the outer
peripheral edge B of a portion of the swelled portion bonded to the end
face of the insulator body is important. Specifically, when the bonded
length l is set at not less than 1 mm but not more than 35 mm, the swelled
portion does not peel from the end face of the insulator body.
The reason therefor will be further explained. When the bonded length l is
small, the terminal end of the bonded interface between the round through
hole 1a and the organic insulating material 3A is directly exposed. When
the surrounding temperature changes, the organic insulating material 3A
expands or shrinks. Since the organic insulating material 3A is firmly
restricted inside the through hole 1a in the radial direction by the wall
surface of the insulator body, the insulating material expands or shrinks
only in the axial direction. Consequently, large tensile stress occurs in
the axial direction of the round through hole 1a near the opening at the
end of the round through hole 1a. If the terminal end of the bonded
interface between the round through hole 1a and the organic insulating
material 3A is directly exposed near the location where the large tensile
stress acts, the bonding forces there is likely to decrease.
On the other hand, the organic insulating material in the swelled portion
4A has room to expand or shrink freely to some degree even in the radial
direction and in the axial direction different from a case where the
insulating material is located inside the round through hole 1a.
Therefore, the stress applied to the outer peripheral edge B of the bonded
portion is far smaller than that acting upon the outer peripheral edge A
of the round through hole 1a. Thus, the organic insulating material is
difficult to peel from the terminal end of the bonded portion.
Furthermore, according to the inventors' investigations, if the bonded
length is too great, the bonding forces are likely to decrease. This is
because when the surrounding temperature changes, the axially displaced
(expanded or shrunk) absolute amount of the swelled portion 4A increases.
As a result, a large tensile stress occurs along the end face 1c at the
outer peripheral edge B of the bonded portion between the organic
insulating material and the end face 1c.
When the bonded length l from the outer peripheral edge A of the round
through hole 1a to the outer peripheral edge B of the bonded portion is
set at not more than 35 mm in accordance with the present invention, a
radially expanded or shrunk absolute amount of the swelled portion 4A
following change in temperature can be reduced. As a result, a tensile
stress occurring at the outer peripheral edge B of the bonded portion
between can be reduced. Accordingly, even when the organic insulating
material 3A expands or shrinks with changes in the surrounding
temperature, the bonding forces at the bonded interface is difficult to
decrease so that the optical fiber composite insulator having excellent
insulating performance for a long term can be obtained.
FIG. 9 is a sectional view for schematically illustrating an entire optical
fiber composite body in which a plurality of insulator bodies 1 are piled
one upon another at plural stages. The same reference numerals in FIGS. 7
and 8 are given to the same parts as in FIGS. 7 and 8. Two or more
insulator bodies 1 are prepared, and integrated by connecting flanges 6 of
the insulator bodies 1 by means of bolts 10. To such a composite insulator
in which the insulator bodies 1 are piled together in plural stages is
applicable the present invention, and a swelled portion 4A can be formed
on an end face 1c of the insulator body.
The shape of the swelled portion may be varied in the form of 4B, 4C or 14
as shown in FIG. 10, 11 or 12. In the embodiment of FIG. 10, an extension
portion 4b is formed at a skirt of an outer peripheral edge of a
frusto-conical portion 4a as in FIG. 7. A flat round top portion 4d is
formed on a central portion of the frusto-conical portion 4a. In the
embodiment of FIG. 11, an extension portion 4b is formed at a skit of an
outer peripheral edge of a frusto-conical portion 4a, too. A recessed
portion 4e is formed in a central portion of the frusto-conical portion 4a
as a top portion. In the embodiment of FIG. 12, a swelled portion 14
consists of a discoidal portion 14a around a through hole 1a as its center
and a columnar top portion 14b formed on a central portion of the
discoidal portion 14a.
When the main portion of the swelled portion 4A, 4B or 4C is shaped in a
frusto-conical form, the following effects can be obtained.
That is, the expansion or shrinkage of the organic insulating material due
to changes in the surrounding temperature is uniformly released in radial
directions, so that the expansion or shrinkage of the organic insulating
material can be reduced in the axial direction. Therefore, the optical
fiber composite insulator having excellent light transmittability and
being free from warping of the optical fiber can be obtained.
In addition, when the top portion of the frusto-conical portion 4a or the
discoidal portion 14a is formed in the columnar shape, the columnar top
portion 4c, 14b shrinks equally in the radial directions and in the axial
direction. However, since the other frusto-conical portion or the
discoidal portion excluding the columnar portion 4c, 14b is bonded to the
end face 1c of the insulator body, the organic insulating material is
difficult to shrink in the radial direction but easy to shrink in the
axial direction. Therefore, the axially shrunk amount of the organic
insulating material at the columnar top portion 4c, 14b becomes smaller
than the axially shrunk amount at the other frusto-conical portion or the
other discoidal portion. Strain occurs inside the organic insulating
material at the root of the columnar top portion 4c, 14b by an amount
corresponding to a difference in shrinkage. In this case, it was
discovered that when a height h of the columnar top portion 4c, 14b is set
at not more than 5 mm, the above shrinkage difference becomes extremely
small, so that no strain occurs inside the organic insulating material
near the root of the columnar top portion 4c, 14b. Owing to this, since no
microbending occurs in the optical fiber near the root of the cylindrical
columnar top portion 4c, 14b, the light transmission loss at low
temperatures can be further decreased. When the top portion is flat at 4
d, the height of the top portion is 0 mm, so that no such a problem
occurs.
When the top portion of the frusto-conical portion 4a or the discoidal
portion 14a is provided with a recess 4e, the expansion of the organic
insulating material in the radial direction is restricted at high
temperatures by a peripheral surface of the recess 4e near the bottom
face of the recess 4e. As a result, the recess is enlarged near the bottom
portion. Accordingly, strain occurs upon a root portion of the optical
fiber projecting from the bottom of the recess.
In this case, when a height h of the recess 4e is set at not more than 5
mm, the radial expansion of the organic insulating material is not
restricted near the bottom surface of the recess 4e and no strain occurs
at the root of the optical fiber, so that the light transmission loss at
high temperature is further reduced.
In FIGS. 7 and 12, the top portion 4c, 14b has a columnar shape. In this
case, it is preferable that the radius of the surface at the top is not
less than 3 mm. By so doing, portions of the optical fibers taken out from
the organic insulating material are reinforced with the top portion 4c,
14b, and even when the optical fibers projecting outwardly from the sealed
portion are swayed due to vibrations resulting from inevitable forces
during working or earthquakes, the optical fibers are not damaged at the
taken-out portions.
Next, a method for producing the optical fiber composite insulators as
shown in FIGS. 7 through 12 will be explained with reference to FIG. 13.
A mold 7 is placed on each of upper and lower end faces 1c of an insulator
body 1. A swelled portion-forming space 7a is formed in the mold 7, and a
through hole 7b is communicated with the swelled portion-forming space 7a.
An organic insulating material-feeding pipe 9A is fitted to the lower mold
7, and an organic insulating material discharge pipe 9B is fitted to the
upper mold 7. The interior of each of the pipes 9A and 9B is communicated
with the through hole 7b. Each mold 7 is fixed to a flange 6 by bolts 10,
and the mold 7 and the end face 1c are gas-tightly sealed by an O-ring 11.
Optical fibers 2 are passed through the optical fiber-inserting hole 7c of
the mold 7, and stretched over through the round through hole 1a. A vacuum
packing 8 is set at the optical fiber-inserting hole 7c of each of the
molds 7.
While the optical fibers 2 are stretched straight under application of
appropriate tensile stress, the interior of the round through hole 1a is
evacuated to vacuum, and an organic insulating material 3B is poured the
material-pouring pipe 9A. The material 3B rises inside the round through
hole 1a, and reaches the material-discharge opening 9B. The swelled
portion-forming space 7a and the round through hole 1a are filled with the
organic insulating material 3B, which is cured by heating. Thereafter, the
molds 7 are removed.
By the above method, the optical fiber composite insulators shown in FIGS.
7 through 12 can be produced at high efficiency. In addition, it is
effective to apply tensile stress upon the optical fiber 2 during the
filling, heating and curing of the material 3B. By so doing, the light
transmittability of the optical fiber can be well maintained through
before and after the curing by the heating.
In the following, concrete experimental results will be explained.
EXPERIMENT 3
Optical fiber composite insulators as shown in FIG. 7 were produced by the
method shown in FIG. 13. As an organic insulating material, addition type
silicone rubber was used, and a heating curing temperature was set at
70.degree. C. to 90.degree. C. The dimensions of the insulator bodies were
950 mm in a total length, 105 mm in a barrel diameter, and 205 mm in a
shed diameter. A bonded length l was 20 mm, and a height of a columnar top
portion 4c was 3 mm. A height H of a swelled portion 4A was varied as
shown in FIG. 14, and a light transmission loss at low temperatures was
measured. Results are shown in FIG. 14.
In FIG. 14, the light transmission loss at 0.degree. C. and the light
transmission loss at -20.degree. C. are shown. The light transmission
losses at 0.degree. C. and -20.degree. C. were obtained as a ratio of a
light-transmitted amount at 0.degree. C. or -20.degree. C. to that at
25.degree. C.
As is seen in FIG. 14, when the height H exceeds 40 mm, the light
transmission loss at low temperatures rapidly increases. This tendency is
almost similarly observed at 0.degree. C. and -20.degree. C.
EXPERIMENT 4
Optical fiber composite insulators were produced in the same manner as in
Experiment 3. The height H of the swelled portion 4A was set at 40 mm, and
the height of the columnar top portion 4c was set at 3 mm. A bonded length
l was varied in various ways as shown in Table 2, and bonding forces
between the organic insulating material and the end face of the insulator
body were evaluated. Specifically, with respect to each sample, three
optical fiber composite bodies were prepared for each bonded length l and
each cycle, and heating/cooling were repeated at a given number of times
to apply cooling/heating cycles between -20.degree. C. and 80.degree. C.
to the insulators. Then, bonding forces between the organic insulating
material and the end face of the insulator body were evaluated. The
bonding forces were evaluated by pulling upwardly the organic insulating
material in the swelled portion and examining whether the organic
insulating material undergoes cohesive failure or the organic insulating
material peeled from the end face of the insulator body. Samples were
evaluated by ".circleincircle." , ".largecircle." and "x". The symbols
".circleincircle.", ".largecircle." and "x" mean the following:
".largecircle." . . . All three insulators underwent cohesion failure
".largecircle." . . . In one or more of three insulators, the organic
insulating material peeled from the insulator end face.
"x" . . . In all three insulators, the organic insulating material peeled
from the insulator end face.
Results are shown in Table 2. As is seen from Table 2, when the bonded
length l is set at 1 to 35 mm, the bonding forces are great.
TABLE 2
______________________________________
Bonded Evaluation of bonding forces of
length organic insulating material
(mm) 1000 cycle 2000 cycle
3000 cycle
______________________________________
Invention
1 .circleincircle.
.circleincircle.
.circleincircle.
Examples 5 .circleincircle.
.circleincircle.
.circleincircle.
10 .circleincircle.
.circleincircle.
.circleincircle.
15 .circleincircle.
.circleincircle.
.circleincircle.
20 .circleincircle.
.circleincircle.
.circleincircle.
30 .circleincircle.
.circleincircle.
.circleincircle.
35 .circleincircle.
.circleincircle.
.circleincircle.
Comparative
0.2 .circleincircle.
.largecircle.
X
Examples 0.5 .circleincircle.
.largecircle.
.largecircle.
40 .circleincircle.
.largecircle.
.largecircle.
80 .circleincircle.
.largecircle.
X
______________________________________
EXPERIMENT 5
Insulator bodies each having a total length of 950 mm, a barrel diameter of
105 mm and a shed diameter of 205 mm were piled at two stages. As an
organic insulating material, silicone rubber was used, and optical fiber
composite insulators as shown in FIG. 7, 10 or 11 were produced. A height
of a swelled portion 4A, 4B, 4C was set at 25 mm, and a diameter of a
bottom surface of a frusto-conical portion 4a was set at 60 mm. A shape
and a height of a top portion were varied as shown in FIG. 15, and light
transmission losses at 80.degree. C. and -20.degree. C. were measured.
Results are shown in FIG. 15. Each of the light transmission losses was
obtained as a ratio of a light-transmitted amount at 80.degree. C. or
-20.degree. C. to that at 25.degree. C.
As is seen from FIG. 15, when the height h is set at not more than 5 mm,
the light transmission loss can be largely reduced. Further, when the
swelled portion of the insulator includes a recessed top portion and the
height h is greater than 5 mm, the light transmission loss at 80.degree.
C. becomes greater. When the insulator is provided with the columnar top
portion (FIG. 7) and the height h is great, the light transmission loss
particularly at -20.degree. C. increases.
As mentioned above, according to the present invention, since the height
from the end face of the insulator body to the tip of the swelled portion
is set at not more than 40 mm, the strain inside the organic insulating
material near the opening at the end of the through hole can be largely
reduced, and microbending of the optical fiber at this portion can be
prevented. Thereby, the light transmission loss at low temperatures can be
largely reduced.
Since the bonding length from the outer peripheral edge of the through hole
to the outer peripheral edge of the bonded portion of the swelled portion
to the end face of the insulator body is set at not less than 1 mm but not
more than 35 mm, reduction in the bonding forces of the swelled portion
can be prevented, so that the optical fiber composite insulators
maintaining excellent insulating performances for a long time can be
obtained.
FIGS. 16 through 18 are sectional views of principal portions of optical
fiber composite insulators according to the third aspect of the present
invention in an enlarged scale. The same reference numerals in FIG. 1 are
given to the same parts as in FIG. 1, and their explanation is omitted.
In the following, a method for producing the composite insulators shown in
FIGS. 16 through 18 will be explained. First, optical fibers 2 are passed
through a through hole 1a of an insulator body 1, and an organic
insulating material is forcedly poured and filled into the through hole 1a
under vacuum. Then, the organic insulating material is cured by heating.
As the organic insulating material, silicone rubber, urethane rubber,
epoxy resin or the like is preferred.
Then, a holder 23 is set on an end face 3d. The holder 23 is formed with,
for example, two columnar insertion holes 23a.Optical fibers 2 projecting
from the end face 3d are stretched straight in a perpendicular direction,
and passed through the respective insertion holes 23a, and the holder is
moved down.
Thereafter, in the case of the embodiment of FIG. 16, an adhesive is
applied to a bottom surface of the holder 23, and the holder 23 is firmly
fixed to the end face 3d through the adhesive layer 26. At that time, the
locations of the insertion holes 23a are aligned with respective taken-out
locations of the end face for the optical fibers 2 so that the optical
fibers may not be bent. Next, non-sealed portions of the optical fibers 2
are inserted through the respective protective tubes 25, and a tip of each
of the protective tubes is inserted into the insertion hole 23a. A part of
the optical fiber is exposed between an end face 25a of the protective
tube 25 and the end face 3d of the organic insulating material. It is
preferable to insert the protective tube 25 into the holder 23 by an
amount equal to about half of the height of the holder 23. The exposed
portion 2a of the optical fiber 2 and the end face 25a of the protective
tube 25 are held in the insertion hole 23a.
In the embodiment illustrated in FIG. 17, the same procedure as in FIG. 16
is effected until the holder 23 is set on the end face 3d. However, after
the holder 23 is set, no adhesive layer 26 is provided different from the
embodiment of FIG. 16, and a cylindrical member 22 is arranged around an
outer periphery of the holder 23, thereby fixing the holder 23. The inner
wall surface of the cylindrical member 22 is butted against the outer
periphery of the holder 23 to hold the holder 23. At that time, it is
preferable that an adhesive layer 21 is provided at the lower end of the
cylindrical member 22, and the cylindrical body 22 is fixedly bonded to
the swelled portion 3 with the adhesive layer. Further, a thermally
shrinkable tube is more preferably used as the cylindrical member 22,
because the holder 23 is more firmly fixed. Thereafter, the non-adhered
portions of the optical fibers 2 are inserted into the protective tubes,
and the tips of the protective tubes 25 are inserted into the respective
insertion holes 23. A part of the optical fiber is exposed between the end
face 25a of the protective tube 25 and the end face 3d of the organic
insulating material. It is preferable that the protective tube 25 is
inserted into the holder 23 by an amount equal to about a half of the
height of the holder 23. The exposed parts of the optical fibers and the
end faces 25a of the protective tubes 25 are held inside the respective
insertion holes 23a.
In the embodiment shown in FIG. 18, the holder 23 is fixed onto the end
face 3d of the insulating material 3 by using an adhesive layer 26 and a
cylindrical member 22. The organic insulating material is cured by
heating. In the same manner as in the embodiment of FIG. 16, the holder 23
is set on the end face 3d, an adhesive is applied to the bottom surface of
the holder 23, and the holder is firmly fixed onto the end face 3d through
an adhesive layer 26. Then, in the same manner as in the embodiment of
FIG. 17, the cylindrical member 22 is arranged around the outer periphery
of the holder 23. Then, in the same manner as in the embodiments of FIGS.
16 and 17, the protective tubes 25 are inserted into the respective
insertion holes 23a of the holder 23.
According to the above embodiments, the locations through which the optical
fibers are taken out are aligned with the locations of the insertion holes
23a, and the exposed portions of the optical fibers 2 and the tip portions
of the protective tubes 25 are held inside the insertion holes 23a.
Therefore, the optical fibers are not bent at all at the exposed portions
2a. Further, since the optical fibers are fixed by the holder near the end
face 25a, no excess load is applied to the optical fiber near the end face
25a even when the protective tube is bent or swayed. Therefore, the
optical fiber composite insulator having excellent light transmittability
can be obtained.
Further, in the embodiment shown in FIG. 18, the holder 25 is fixed to the
end face 3d by means of the adhesive layer 26, the cylindrical member 22,
and the adhesive 21. Therefore, as compared with the embodiment in FIGS.
16 and 17, the holder 23 is more firmly fixed onto the end face 3d so that
the optical fiber composite insulator provided with the protective tube 25
having greater resistance to the bending or swaying and possessing stably
excellent light transmittability can be obtained.
Furthermore, in the embodiment of FIG. 18, the holder 23 is held inside the
cylindrical body 22, a molding layer 24 is formed on the holder 23, and
the protective tubes 25 are further fixed by the molding layer 24. Thus,
the movement of the protective tubes 25 is further restricted on the upper
side of the protective tube 23, so that even when the protective tube is
swayed or bent, such does not almost influence near the end face 25a.
Thereby, the light transmission loss can be further reduced.
The dimension of the holder 23 may be changed in various ways. In general,
it is preferable that the diameter is set at 5 to 20 mm, and the height is
set at 3 to 15 mm. The holder 23 may be made of a rubbery elastic
material, and the diameter of the insertion hole 23c may be substantially
equal to or smaller by up to about 0.6 mm than the outer diameter of the
protective tube 25. When the holder 23 is made of the rubbery elastic
material and the diameter of the insertion hole 23 is made smaller than
the outer diameter of the protective tube 25, the tip of the protective
tube 25 is inserted into the insertion hole 23c, while the opening of the
insertion hole 23c is slightly being widened. In this case, the tip
portion of the protective tube is pressed and fixed by shrinking forces of
the rubbery elastic material, the location of the protective tube on the
end face is more difficult to deviate. Therefore, the light
transmittability is further improved.
As the organic insulating material 3, silicone rubber, urethane rubber,
epoxy resin or the like is preferred. As a material for the protective
tube 25, teflon or silicone rubber is preferably used, because such
improves durability. As the rubbery elastic material capable of
constituting the holder, silicone rubber, urethane rubber, butyl rubber,
ethylene.propylene rubber, hyparon, or the like is preferred.
In the embodiment of FIG. 19, the holder 23 is bonded to the end face 3d in
the same manner as in FIG. 16. However, in FIG. 19, the adhesive layer 26A
is provided only on the bottom surface of the holder 23 and the peripheral
edge portion of the end face 3d in an annular shape, while a space is
defined inside the adhesive layer 9A.
In an embodiment of FIG. 20, a bottom face of a holder 23 is directly
contacted with the end face 3d, and the holder 23 is bonded to the end
face by applying an adhesive onto a lower outer peripheral surface of the
holder 23 and an upper outer peripheral surface of a columnar top portion
3c. Further, a molding layer 24A is directly swelled upwardly from an
upper end face of the holder 23.
In an embodiment of FIG. 21, a round recess 27 is formed in a central
portion of a frusto-conical portion 3a, and a lower half portion of a
holder 23 is fixedly received in the recess 27. An adhesive 26C is applied
to an exposed outer peripheral surface of the holder 23 to fix the holder
to an upper face of an organic insulating layer 3, and molding layer 24A
is heaped on an upper end face of the holder 23.
In an embodiment of FIG. 22, a round recess 28 is provided in a central
portion of a columnar top portion 3c. A round recess 23b is also provided
in a lower end portion of the holder 23, and the recess 27 is opposed to
the recess 23b. The holder 23 is bonded to the columnar top portion 3c
with an adhesive 26A, and the outer peripheries of the holder 23 and the
columnar top portion 3c are held by a cylindrical member 22. A lower end
of the cylindrical member 22 is bonded to the organic insulating material
with an adhesive 21. A molding layer 24 is provided on an upper side of
the holder 23 inside the cylindrical body 22.
In the following, experimental results will be concretely explained.
EXPERIMENT 6
With respect to each of the embodiments shown in FIGS. 16, 17 and 18, five
optical fiber composite insulators were prepared, and a light-transmitted
amount before the treatment of end portions and that after the treatment
of the end portions were measured with respect to each optical fiber
composite insulators. Ratio between the light-transmitted amounts before
and after the treatment are shown in Table 3 as changes in the light
transmission losses due to the treatment of the end portions.
TABLE 3
______________________________________
Change in light transmission
loss through the treatment
of the ends
(Amount of transmitted light
after treatment of ends/
Sample Amount of transmitted light
No. before treatment of ends)
______________________________________
FIG. 16
1 0.96 Invention
2 0.98 Examples
3 0.97
4 0.97
5 0.99
FIG. 17
6 0.94
7 0.97
8 0.96
9 0.95
10 0.94
FIG. 18
11 0.67 Comparative
12 0.74 Examples
13 0.58
14 0.82
165 0.71
______________________________________
It is seen from Table 3 that the average light transmission loss is
conspicuously large in the case of Sample Nos. 11-15, and ranges from 0.58
to 0.82 with great variations.
EXPERIMENT 7
With respect to each of the embodiments of FIGS. 16, 17 and 18, five
optical fiber composite insulators were prepared, and a holding force of
the holder was measured with respect to each optical fiber composite
insulator. As the holding forces were taken forces at which the holder
began to slip in case that forces were applied from a peripheral side of
the holder. Results are expressed as relative values by taking the holding
forces of the holder in FIG. 18 as 100. The average value for the five
insulators is shown in Table 4 with respect to each embodiment. As a
result, it is seen that the holding forces of the holder in the embodiment
of FIG. 18 is greatest.
TABLE 4
______________________________________
FIG. 16 FIG. 17 FIG. 18
______________________________________
Holder-holding power
93 71 100
______________________________________
According to the present invention, the holder is placed on the end face of
the organic insulating material, the locations of the insertion holes of
the holder are aligned with the locations through which the optical fibers
are taken out, and a part of each of the protective tube is held inside
the insertion hole. Thus, the optical fiber is not bent at an exposed
portion. Further, since the protective tubes are fixed by the holder near
the end faces, no excess load is applied to the optical fiber near the end
face even when the protective tube is bent or swayed. Thus, the optical
fiber composite insulators having excellent light transmittability can be
obtained.
In the following, the fourth aspect of the present invention will be
explained, which is directed to a method for producing the optical fiber
composite insulators. The producing method will be explained based on an
optical fiber composite insulator as shown in FIG. 8. First, a through
hole 1a is provided in a central portion of an insulator body 1, and then
at least one optical fiber (in this embodiment, two optical fibers) is
passed through the through hole 1a. In this state, the entire insulator
body 1 is held at a given temperature not lower than 70.degree. C. to
preliminarily heat the insulator body. Thereafter, a given organic
insulating material 3 is filled into the through hole 1a. As the organic
insulating material, silicone rubber, urethane rubber, epoxy resin or the
like is favorably used. Then, the filled organic insulating material 3 is
cured by heating it at a temperature from 75.degree. C. to 90.degree. C.
Thereby, the optical fiber composite insulator is obtained. When the
organic insulating material is filled into the through hole 1a of the
insulator body 1, the optical fiber passed through the through hole is
stretched straight, and the optical fiber is kept straight stretched until
the organic insulating material is cured.
The producing method according to the present invention may be also applied
to two-stage piled optical fiber composite insulators as shown in FIG. 9
and multiple-stage piled optical fiber composite insulators.
EXPERIMENT 7
In order to examine influences of the preliminarily heating temperature of
the entire insulator body and the curing temperature of the organic
insulating material upon the insulators, optical fiber composite
insulators were prepared by varying the above temperatures in various ways
as shown in Table 5, and their influences were evaluated. At that time,
the insulators each had a total length of 950 mm, a barrel diameter of 105
mm, a shed diameter of 205 mm, and an inner diameter of the through hole
of 5 to 10 mm. As the optical fibers, quartz base optical fiber filaments
were used. On the production of the optical fiber composite insulator, the
optical fibers were passed through the through hole of the insulator body,
and then the entire insulator body was preliminarily heated at a given
temperature not lower than 70.degree. C. for not less than 3 hours.
At a point of the time when the preliminary heating of the insulator was
terminated, the temperature was kept at not less than 70.degree. C., and a
liquid silicone rubber was forcedly fed under pressure of 3 to 10
kgf/cm.sup.2 into the through hole of the insulator body at a vacuum
degree of not more than 5 torr. If the preliminarily heating temperature
is different from the curing temperature of the silicone rubber, it is
preferable to charge the silicone rubber a few to several hours after a
heating kiln is heated up to a given curing temperature. When the
preliminarily heating temperature is higher than 90.degree. C., it takes a
time for the insulator to reach the curing time of the rubber. Thus, the
preheating temperature is preferably not more than 90.degree. C. After the
charging of the silicone rubber was finished, the insulator was kept at
the curing temperature for not less than 3 hours to cure the silicone
rubber by heating. Finally, light transmission losses of each of the
optical fiber composite insulators at low and high temperatures
(-20.degree. C. and 80.degree. C.) were obtained as the respectively
average values of ten insulators. Results are shown in FIG. 23. The light
transmission loss was obtained as a ratio of a light-transmitted amount at
ordinary temperature (25.degree. C.) and the light-transmitted amount at
each temperature (-20.degree. C. or 80.degree. C.).
TABLE 5
______________________________________
Curing temperature
of organic Preheating
insulating material
temperature
Sample No. (.degree.C.) (.degree.C.)
______________________________________
Invention 1 75 70
samples 2 80 75
3 85 85
4 90 85
Comparative
1 90 65
samples 2 70 not preheated
3 110 85
______________________________________
It is seen from the results in FIG. 23 that the invention samples in which
the preliminarily heating temperature was not less than 70.degree. C. and
the curing temperature of the organic insulating material was not less
than 75.degree. C. but not more than 90.degree. C. exhibited lower light
transmission losses at both the low temperature and high temperature as
compared with comparative samples in which the above requirements were not
satisfied in some respect.
As is clear from the above explanation, according to the present invention,
since the entire insulator is preliminarily heated at not less than
70.degree. C. and the organic insulating material is cured by heating at
not less than 75.degree. C. but not less than 90.degree. C., the expanded
amount and the shrunk amount of the organic insulating material at the
time of curing can be reduced, so that the optical fibers having excellent
light transmittability can be obtained.
In the fourth aspect of the present invention, optical fiber composite
insulators as shown in FIGS. 8 and 9 can be produced by using a device as
shown in FIG. 13. In the producing method of the invention, optical fibers
2 are passed through a through hole 1a of the insulator body, and each of
upper and lower end portions of the insulator body 1 is fitted to a flange
6 at the outer peripheral surface through a cement layer 5. An organic
insulating layer 3A is filled into the through hole 1a. The organic
insulating material 3A is swelled up from an end face of each of upper and
lower ends of the insulator body 1 to form a swelled portion 4. As the
organic insulating material 3, silicone rubber, urethane rubber, epoxy
rubber or the like may be recited by way of example.
In the embodiment of FIG. 8, a single insulator body 1 is used, whereas in
the embodiment of FIG. 9, for example, two insulator bodies are integrated
by piling these insulator bodies 1 and integrating them by connecting the
flanges 6 with bolts 10.
By using the producing method of the invention, the swelled portions having
various shapes as shown in FIGS. 7, 11 and 12 can be formed.
In the embodiment in FIG. 7, the swelled portion consists of three
portions. That is, a frusto-conical portion 4a is formed concentrically
with the through hole 1a, a columnar top portion 4c is formed on a central
portion of the frusto-conical portion 4a, and a relatively thin extension
portion 4b is formed at a skirt of the frusto-conical portion 4a. The
optical fibers 2 are passed through the frusto-conical portion 4a and the
columnar top portion 4c, and is taken out from a tip face of the columnar
top portion 4c. In the swelled portion 4A shown in FIG. 11, the
frusto-conical portion 4a is the same as that in FIG. 7, but the shape of
the top portion is different from that of the top portion in FIG. 7. The
shape of the top portion in FIG. 11 is not of a cylindrical column but a
recess 4d is formed on a top face.
In the swelled portion 14 shown in FIG. 12, a flat discoidal portion 14a is
formed on an end face 1c, and a columnar top portion 14b is formed in a
central portion of the discoidal portion 14a. The optical fibers 2 are
straight taken out from an end face of the columnar top portion 14b in the
perpendicular direction.
The composite insulators shown in FIGS. 7, 11 and 12 can be produced at
high efficiency according to the producing method of the present
invention.
The organic insulating material 3B is filled into the through hole 1a in
the state that the optical fiber passed through the through hole is
stretched straight, and this state is kept until the organic insulating
material 3B is cured. As a result, the optical fiber 2 is not finely bent
due to the filling pressure of the organic insulating material or the
shrinkage of the material 3B following the curing. Thus, the light
transmission loss of the optical fiber is reduced, and even when the
organic insulating material 3A expands or shrinks due to changes in the
temperature, fatigue fracture of the optical fiber 2 is difficult to
occur.
When the optical fiber passed through the through hole is to be stretched
straight, it is preferable to set the elongation of the optical fiber at
not less than 0.1% but not more than 1%. When the optical fiber is
stretched at an elongation of less than 0.1%, the insulator is not so
influenced by the charging pressure of the organic insulating material.
However, the insulator is likely to be influenced by the shrinkage of the
organic insulating material due to curing, and there is a tendency that
microbending tends to occur in the optical fiber. Further, when the
optical fiber is stretched at an elongation of more than 1%, the optical
fiber is sealingly fixed with the organic material in the state that the
optical fiber is kept stretched to an unnecessarily great extent. When the
load applied to the optical fiber is removed after the organic insulating
material is cured, the optical fiber is not uniformly shrunk in that a
portion of the optical fiber fixed with the organic insulating material
shrinks differently from that of a portion of the optical fiber not
covered with the organic insulating material. Thus, the light transmission
loss increases and the service life is likely to be shortened.
In the following, concrete experimental results will be described.
EXPERIMENT 8
Optical fiber composite insulators as shown in FIGS. 7 and 8 were prepared
by using the device shown in FIG. 13. As an organic insulating material,
liquid silicone rubber was used, and a heating-curing temperature and time
were set at 70.degree. C. to 90.degree. C. and 3 to 8 hours, respectively.
The dimensions of each insulator body was 950 mm in an entire length, 105
mm in a barrel diameter, and 205 mm in a shed diameter. As the optical
fiber 2, two quartz base optical fiber filaments were used.
In Sample Nos. 1 through 5 in Table 8, while a tensile load was applied to
each of the optical fibers 2 to give an elongation of 0.2% to 0.8%,
silicone rubber was filled, and cured by heating. In Control Sample Nos. 6
through 9, while the optical fibers 2 were not particularly pulled and
kept hanged in a natural state, the organic insulating material was
filled, and cured. With respect each sample, the light transmission loss
change amounts and the light-transmitted amount after a cooling/heating
repetition test were evaluated. Results are shown in Table 6.
The light transmission loss change amounts were each obtained as a ratio of
a minimum light-transmitted amount to a maximum light-transmitted amount
in a temperature range of -20.degree. C. to 80.degree. C. The
light-transmitted amount after the cooling/heating repetition test was
evaluated as follows. That is, each optical fiber composite insulator was
subjected to cycles in which the insulator was immersed into a low
temperature vessel at -20.degree. C. and a high temperature vessel at
80.degree. C. per one cycle, by a number of times as given in Table 6, and
then the light-transmitted amount at room temperature (25.degree. C.) was
measured. The evaluation results are shown by ".circleincircle.",
".largecircle." or "x". ".circleincircle.", ".largecircle." and "x" means
the following.
".circleincircle." . . . The light-transmitted amount measured at
25.degree. C. was not less than 80% of the initial light-transmitted
amount.
".largecircle." . . . The light-transmitted amount measured at 25.degree.
C. was less than 80% but not less than 50% of the initial
light-transmitted amount.
"x" . . . The light-transmitted amount measured at 25.degree. C. was less
than 50% of the initial light-transmitted amount.
TABLE 6
__________________________________________________________________________
Change amount
of loss of
transmitted
Amount of transmitted light after
Sample
light repeated cooling-heating test
No. (-20-80.degree. C.)
200 cycle
500 cycle
1000 cycle
1500 cycle
__________________________________________________________________________
Examples
1 0.93 .circleincircle.
.circleincircle.
.circleincircle.
.circleincircle.
2 0.91 .circleincircle.
.circleincircle.
.circleincircle.
.circleincircle.
3 0.96 .circleincircle.
.circleincircle.
.circleincircle.
.circleincircle.
4 0.93 .circleincircle.
.circleincircle.
.circleincircle.
.circleincircle.
5 0.94 .circleincircle.
.circleincircle.
.circleincircle.
.circleincircle.
Comparative
6 0.55 .circleincircle.
.largecircle.
.largecircle.
X
Examples
7 0.53 .circleincircle.
.largecircle.
.largecircle.
.largecircle.
8 0.50 .circleincircle.
.circleincircle.
.largecircle.
X
9 0.61 .circleincircle.
.circleincircle.
.largecircle.
X
__________________________________________________________________________
As is clear from the results in Table 6, according to the present
invention, the light transmission loss change amounts can be reduced, the
light-transmitted amounts after the cooling/heating repetition test can be
increased, and the service life of the optical fiber composition insulator
can be prolonged.
EXPERIMENT 9
Each optical fiber composite insulator was prepared in the same manner as
in Experiment 8. A swelled portion 14 as shown in FIG. 12 was employed. As
shown in FIG. 24, the elongation at which the optical fibers 2 are pulled
was varied in various ways. In Sample B, upper and lower ends of the
optical fiber 2 were each fixed to a point such that no tensile stress
might be applied to the optical fiber. In Sample C, only an upper end of
the optical fiber 2 was fixed to a point so that the optical fiber might
be spontaneously hanged down by gravitational forces. With respect to each
plot shown in FIG. 24, ten samples were prepared by trial.
As shown in FIG. 24, while the elongation was varied, the light
transmission loss change amount of each sample was evaluated. The light
transmission loss change amount was obtained as a ratio of a minimum
light-transmitted amount to a maximum light-transmitted amount in a
temperature range between -20.degree. C. and 80.degree. C., and the
average value of ten samples is shown.
As is clear from the results in FIG. 24, since the optical fiber is pulled
according to the present invention, the light transmission loss change
amount is reduced. Further, the elongation of the optical fiber is set
preferably at an amount of 0.1 to 1.0%, more preferably at an amount of
0.2 to 0.8%.
According to the present invention, while the optical fiber is stretched
straight, the organic insulating material is filled into the through hole
of the insulator body, and the optical fiber is kept stretched straight
until the organic insulating material is cured. As a result, the optical
fiber becomes difficult to be finely bent owing to the filling pressure of
the organic insulating material or the shrinkage of the organic insulating
material following the curing. Thereby, the light transmission loss of the
optical fiber can be reduced, and the fatigue fracture of the optical
fiber is not likely to occur even when the organic insulating material
expands or shrinks with changes in the temperature.
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